Studying the Surface Layer Structure of 40Cr Steel after Rough and Semi-Finished Machining

The results of studies of the microstructure and local fields of internal stresses arising in the surface layer of 40Cr steel samples processed in two modes: rough and semi-finished (chip removal to a depth of 1.0 and 0.5 mm, respectively) are presented. The internal structure of all morphological steel components is investigated. The scalar dislocation density and the width of the bending extinction contours are measured and calculated, from which the amplitude of the curvature torsion of the crystal lattice of the forming phases, the excess dislocation density, and the amplitude of internal stresses in different sections of the material are determined. In the initial state, the 40Cr steel matrix is α phase, a solid solution of carbon and alloying elements in α-Fe with a body-centered cubic (bcc) lattice. The morphological components of the α phase are lamellar perlite and ferrite. Rough machining leads to the formation of secondary fragmented perlite. After semi-finishing, lamellar perlite is formed with curved cementite plates.